10 research outputs found
Modeling and Reduction of High Frequency Scatter Noise at LIGO Livingston
The sensitivity of aLIGO detectors is adversely affected by the presence of
noise caused by light scattering. Low frequency seismic disturbances can create
higher frequency scattering noise adversely impacting the frequency band in
which we detect gravitational waves. In this paper, we analyze instances of a
type of scattered light noise we call "Fast Scatter" that is produced by motion
at frequencies greater than 1 Hz, to locate surfaces in the detector that may
be responsible for the noise. We model the phase noise to better understand the
relationship between increases in seismic noise near the site and the resulting
Fast Scatter observed. We find that mechanical damping of the Arm Cavity
Baffles (ACBs) led to a significant reduction of this noise in recent data. For
a similar degree of seismic motion in the 1-3 Hz range, the rate of noise
transients is reduced by a factor of ~ 50.Comment: 23 pages, 19 figure
Large-angle scattered light measurements for quantum-noise filter cavity design studies
Optical loss from scattered light could limit the performance of
quantum-noise filter cavities being considered for an upgrade to the Advanced
LIGO gravitational-wave detectors. This paper describes imaging scatterometer
measurements of the large-angle scattered light from two high-quality sample
optics, a high reflector and a beam splitter. These optics are each
superpolished fused silica substrates with silica:tantala dielectric coatings.
They represent the current state-of-the art optical technology for use in
filter cavities. We present angle-resolved scatter values and integrate these
to estimate the total scatter over the measured angles. We find that the total
integrated light scattered into larger angles can be as small as 4 ppm.Comment: 11 pages, 9 figure
Angular control of optical cavities in a radiation-pressure-dominated regime: the Enhanced LIGO case
We describe the angular sensing and control (ASC) of 4 km detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO). Enhanced LIGO, the culmination of the first generation LIGO detectors, operated between 2009 and 2010 with about 40 kW of laser power in the arm cavities. In this regime, radiation-pressure effects are significant and induce instabilities in the angular opto-mechanical transfer functions. Here we present and motivate the ASC design in this extreme case and present the results of its implementation in Enhanced LIGO. Highlights of the ASC performance are successful control of opto-mechanical torsional modes, relative mirror motions of ≤ 1×10^−7  rad rms, and limited impact on in-band strain sensitivity
Observation of Parametric Instability in Advanced LIGO
Parametric instabilities have long been studied as a potentially limiting
effect in high-power interferometric gravitational wave detectors. Until now,
however, these instabilities have never been observed in a kilometer-scale
interferometer. In this work we describe the first observation of parametric
instability in an Advanced LIGO detector, and the means by which it has been
removed as a barrier to progress
First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO
Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude
First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO
Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude